The following abbreviations are herewith defined, at least some of which are referred to within the following description of the prior art and the present invention.
BSC Base Station Controller
BTS Base Transceiver Station
CNN Core Network Node
CN Control Node
CPU Central Processing Unit
GPRS General Packet Radio Service
IMSI International Mobile Subscriber Identity
IOS Interoperability Specification
MSC Mobile Switching Center
NRI Network Reference Identifier
RAN Radio Access Network
SNSF Serving Node Selection Function
UTIL CPU Utilization
VLR Visiting Location Register
A wireless telecommunications network is normally divided into an access network and a core network. In one type of a wireless telecommunications network, the access network includes Base Transceiver Stations (BTSs) and control nodes such as Base Station Controllers (BSCs), while the core network includes core network nodes (CNN) such as Mobile Switching Centers (MSCs), Visiting Location Registers (VLRs), Home Location Registers (HLRs), and a GPRS Support Node (GSN) if the wireless telecommunications network supports GPRS.
Typically, each BSC (control node) in a specific geographical area of the access network is served by one specific MSC (core network node). This means that each BSC always communicates with one dedicated MSC that serves the specific geographical area (MSC Service Area) of the wireless telecommunications network. When a mobile station requests a service from the wireless telecommunications network it will be registered with the dedicated MSC of the current geographical area (MSC Service Area) by the BSC. The subscriber information of the mobile subscriber, that is using the mobile station, is stored in the VLR that serves the dedicated MSC, i.e. the mobile station is registered in this VLR. It is a common practice to combine the VLR with the MSC into a MSC/VLR, which means that the mobile station is registered in a MSC/VLR.
A new type of architecture for a wireless telecommunications network is to create a pool of core network nodes, e.g. a pool of MSC/VLR's, that is connected to one or more access networks, e.g. to control nodes (BSCs). This means that each BSC/BTS can access a number of MSC/VLR's and that a MSC/VLR in a pool of MSC/VLR's can serve a mobile station in a larger geographical area than in a “normal” MSC service area. The service area that is supported by all MSC/VLR's in the MSC-pool is called the MSC-pool service area. In this case, the MSC service area of each MSC/VLR in the pool will be the same area as the MSC-pool service area. A pool of core network nodes is also called a CNN-pool. If it is a pool of MSC/VLR's then it is called a MSC-pool for simplicity.
There are several advantages associated with using this “pooled” architecture which are as follows:                Reduction in the amount of inter-MSC handovers.        Full MSC/VLR redundancy in the case of loss due to natural disaster, hardware or software failure, or required maintenance actions.        Reduction in the inter-MSC/VLR location updates.        Reduction in the number of HLR updates.        Reduction in the number of hard handoffs.        
A wireless telecommunications network having a pool of MSC/VLRs provides a solution for maintaining a network where MSC/VLR redundancy exits. This wireless telecommunications network includes all of the necessary signaling connections between each one of the BSCs with multiple MSCs, so that mobile stations served by any BSC of that MSC-pool serving area could be served by any MSC/VLR within the MSC-pool. Under this configuration, when one MSC/VLR in the pool goes out-of-service due to a natural disaster, hardware failure, software failure, etc. . . . , then the other MSC/VLRs in the MSC-pool can continue to provide service with little or no delay to the registered mobile stations.
Within this type of wireless telecommunications network, there is a necessary function where each mobile station that requests service from the MSC-pool serving area must upon registration (explicit/implied) be assigned to a MSC/VLR. How this function assigns mobile stations to the MSC/VLR is important because this initial mobile station-to-MSC/VLR mapping provides the necessary load-distribution (and load-balancing) amongst the MSC/VLRs within the MSC-pool.
This initial mobile station assignment happens when a mobile station powers up in the MSC-pool service area of the MSC-pool or roams from another service area into the MSC-pool service area of the MSC-pool. The initial mobile station assignment responsibility is handled by a management device (also referred to in the art as a service node selection function, a selection function, or a core node selection function) which uses a distribution algorithm to select a MSC/VLR within the MSC-pool.
In addition to the initial mobile station assignment, the management device may have the responsibility to initiate a redistribution of mobile station information between the MSC/VLRs in the MSC-pool, e.g., register the mobile station with another MSC/VLR within the MSC-pool when an unbalanced MSC-pool is detected during normal operations and runtime events. For example, there may be an unbalanced MSC-pool when a MSC/VLR (or any of its components) is brought back in-to-service after being out-of-service for maintenance (hardware or software), a MSC/VLR upgrade, MSC/VLR hardware additions/removal, or when a new MSC/VLR is added to the MSC-pool. This reassignment should not affect the end users' experience with the mobile station, especially with respect to service availability and reachability. The existing management device may work well in certain situations but there is always a desire to improve the management of the initial mobile station assignment to individual MSC/VLRs in the MSC-pool and/or the management of the redistribution of mobile stations between the MSC/VLRs in the MSC-pool when an unbalanced MSC-pool is detected during normal operations and runtime events.